Embodiments of the present invention relate to a double-drum sequential gear control device for a motor-vehicle gearbox. The gear control device includes a first rotary drum associated with a first secondary shaft of the gearbox in order to bring about the movement of one or more engagement sleeves arranged slidably on that shaft, a second rotary drum associated with a second secondary shaft of the gearbox in order to bring about the movement of one or more engagement sleeves arranged slidably on that shaft, and an actuation unit arranged to bring about rotation of the first drum and of the second drum in a synchronized manner. The two drums are rotatably mounted about respective rotation axes which are parallel to but not coincident with each other. More particularly, embodiments of the invention relate to a method for the “phase setting” of the two drums of the above-mentioned gear control device, that is, for positioning them in the correct relative angular position, during the mounting of the control device on the gearbox.
In the following description and claims, the expression “angular position” is intended to relate to the rotary movement of each drum about its rotation axis. In a gear control device such as that defined above, in which both drums are rotated by the same actuation unit which typically comprises an electric motor and a geared transmission mechanism interposed between the electric motor and the two drums, problems may arise at the mounting stage of positioning the two drums with the correct relative orientation to ensure that, in operation, the gear control device can conform to the required gear shift sequence and, above all, does not perform incorrect control operations with the risk of causing damage not only to the gear control device but also to the gearbox.
United States Pre-Grant Publication Number US2006/162487 provides a sequential gear control device for a motorcycle gearbox comprising a single rotary drum made up of two drum portions which are arranged coaxially with each other and are fixedly connected for rotation with each other by means of a plurality of locking pins. The locking pins ensure the correct relative angular position between the two drum portions of the single drum.
United States Pre-Grant Publication Number US2007/0209460 provides a double-drum sequential gear control device for a motor-vehicle of the same type as the one to which the method of the present application is directed, i.e. a sequential gear control device for a motor-vehicle comprising separate first and second drums which are rotatably mounted about respective first and second rotation axes parallel to each other.